U.S. patent number 7,103,134 [Application Number 10/330,049] was granted by the patent office on 2006-09-05 for computed tomography apparatus.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Tatsuro Suzuki.
United States Patent |
7,103,134 |
Suzuki |
September 5, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Computed tomography apparatus
Abstract
A computed tomography apparatus configured to assist an operator
in easily and correctly making an imaging plan thereby reducing the
burden of the operator. The computed tomography apparatus selects
at least one of reconstruction methods or changes a parameter by
the information the operator inputs or displays its grade
information, for example.
Inventors: |
Suzuki; Tatsuro (Tochigi-ken,
JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Tokyo, JP)
|
Family
ID: |
26625366 |
Appl.
No.: |
10/330,049 |
Filed: |
December 30, 2002 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20030123603 A1 |
Jul 3, 2003 |
|
Current U.S.
Class: |
378/4;
378/901 |
Current CPC
Class: |
A61B
6/032 (20130101); A61B 6/4085 (20130101); A61B
6/469 (20130101); A61B 6/488 (20130101); A61B
6/027 (20130101); Y10S 378/901 (20130101) |
Current International
Class: |
A61B
6/03 (20060101) |
Field of
Search: |
;378/4,15,16,901 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Glick; Edward J.
Assistant Examiner: Suchecki; Krysytna
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A computed tomography apparatus, comprising: a radiation source
configured to emit a radiation through an object; a detector
configured to detect the radiation passed through the object and
output a corresponding output signal; a data collection unit
configured to collect projection data based on the output signal of
the detector; and a controller configured to control a display so
as to display at least one of a plurality of reconstruction methods
and corresponding reconstruction method grade information defining
a qualitative factor characteristic of imaging performed by the
respective at least one of a plurality of reconstruction methods on
said display.
2. The computed tomography apparatus according to claim 1, wherein
the grade information comprises a qualitative factor related to at
least one of: a radiation dose; a scanning time; a total time from
scan to reconstruction; a quality of image; and an over load
protection of the radiation source.
3. The computed tomography apparatus according to claim 1, wherein
each of the displayed reconstruction methods comprises: a name; and
a reconstruction method parameter.
4. The computed tomography apparatus according to claim 1, further
comprising: an image slice width input device configured to input
an image slice width of the object, wherein the controller is
additionally configured to automatically select at least one
candidate reconstruction method from a plurality of candidate
reconstruction methods according to criteria corresponding to the
inputted image slice width and display the selected reconstruction
method on the display.
5. The computed tomography apparatus according to claim 1, wherein
the plurality of candidate reconstruction methods include comprise:
a fan-beam reconstruction method where the image is reconstructed
on the assumption the radiation is perpendicular to a body axis of
the object; and a cone-beam reconstruction method where the image
is reconstructed on basis of the angle of the radiation.
6. The computed tomography apparatus according to claim 1, wherein
the detector comprises: a plurality of detection elements arranged
in two perpendicular directions and configured to output detection
element signals.
7. The computed tomography apparatus according to claim 6, further
comprising: a signal additional unit configured to add the
detection elements signals or add the projection data collected by
the data collection unit along an object axis.
8. The computed tomography apparatus according to claim 1, further
comprising: a main data processing unit configured to perform a
helical compensation to the projection data before an image is
reconstructed.
9. A computed tomography apparatus, comprising: a radiation source
configured to emit a radiation through an object; a detector
configured to detect the radiation passed through the object and
output a corresponding output signal; a data collection unit
configured to collect projection data based on the output signal of
the detector; an input device configured to input an image slice
width of the object; a controller configured to perform a priority
processing in which a reconstruction method is set according to an
order of priority of at least one predetermined feature of the
reconstruction method so as to produce a processing result; and a
reconstruction unit configured to reconstruct an image of the
object on the basis of the projection data with a selected
reconstruction method selected according to the image slice width
and the processing result.
10. The computed tomography apparatus according to claim 9, wherein
the at least one predetermined feature of each reconstruction
method comprises at least one of: a radiation dose; a scanning
time; a total time from scan to reconstruction; a quality of image;
and an over load protection of the radiation source.
11. The computed tomography apparatus according to claim 9, wherein
the detector comprises: a plurality of detection elements arranged
in two perpendicular directions and configured to output detection
element signal.
12. The computed tomography apparatus according to claim 11,
further comprising: a signal additional unit configured to add the
detection elements signals or add the projection data collected by
the data collection unit along an object axis.
13. The computed tomography apparatus according to claim 9, further
comprising: a main data processing unit configured to perform a
helical compensation to the projection data before an image is
reconstructed.
14. A computed tomography apparatus, comprising: a radiation source
configured to emit a radiation through an object; a detector
including a plurality of detection elements configured to detect
the radiation passed through the object and output an output
signal; a data collection unit configured to collect projection
data based on the output signal of the detector; a movement
mechanism configured to move the detector toward the object
helically with a helical pitch; an input device configured to
change a number of image slices of the object; and a controller
configured to give an alarm configured to alert an operator to
confirm the helical pitch when the number of image slices is
changed.
15. A computed tomography apparatus, comprising: a radiation source
configured to emit a radiation through an object; a detector
including a plurality of detection elements configured to detect
the radiation passed through the object and output an output
signal; a data collection unit configured to collect projection
data based on the output signal of the detector; an input device
configured to change a reconstruction thickness of an image of the
object; and a controller configured to give an alarm configured to
alert an operator to confirm an image pitch when the reconstruction
thickness is changed.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 U.S.C. .sctn. 119 to
Japanese patent application No. P2001-399359 filed Dec. 28, 2001
and Japanese patent application No. P2002-353873 filed Dec. 5,
2002, the entire contents of which are incorporated by reference
herein.
BACKGROUND OF THE INVENTION
The present invention relates to a computed tomography apparatus
which takes an image of an object and can reduce the burden of an
operator who makes an imaging plan.
An example of a computed tomography apparatus is an X-ray
computed-tomography apparatus (hereafter called X-ray CT
apparatus). A specific implementation of an X-ray CT apparatus, a
multi-slice X-ray CT apparatus has been developed and has found
widespread use in recent years. A multi-slice X-ray CT apparatus
has a 2-dimensional detector including M channels of N segments
detection elements where a plurality of channel detection elements
are arranged along the segment direction perpendicular to the
channel direction. A multi-slice X-ray CT apparatus collects an
image which is characterized by having high resolution and wide
range. Examples of multi-slice X-ray CT apparatus include 4 slice
type, 8 slice type, and 16 slice type devices . . .
An example of a reconstructing method used with the multi-slice
X-ray CT apparatus is a fan-beam reconstruction method which
reconstructs the image on the assumption an X-ray beam is parallel
to a direction perpendicular to a slice direction although the
X-ray beam is, to be exact, a cone-like X-ray beam (cone-beam)
which spreads in the slice direction. Another example of a
reconstructing method is a cone-beam reconstruction method which
reconstructs the image on basis of the angle of the cone-beam. The
cone-beam reconstruction method is used when the number of slices
to be simultaneously detected equal 8 and the fan-beam
reconstruction method is used when the number of slices equal
4.
There are merits and demerits in these reconstruction methods,
respectively. For example, the cone-beam reconstruction method
makes excellent quality images but requires a longer reconstruction
time as compared with the fan-beam reconstruction method because of
the need to account for the cone angle. Thus, it is necessary for
an operator to understand the special features of each of these
reconstruction methods when choosing an appropriate reconstruction
method for each patient and for specific images of patients.
Setting up the equipment between shots with different methods is
very difficult for an operator. Even if the operator is
well-skilled in setting up the equipment, this set-up process takes
much time and the patient processing efficiency (patient
throughput) decreases. Although conventional imaging plan systems
configured to assist the operator are known, they do not urge the
operator to determine the reconstruction method according to
scanning conditions.
In addition, there is another factor which causes a decrease in
patient throughput. Another example of a multi-slice X-ray CT
apparatus is a multi-slice (e.g., 4 slice or 8 slice) helical X-ray
CT apparatus which performs a helical scan. With a multi-slice
helical apparatus, the operator can choose the image slice width,
thereby creating an imaging plan. The image slice width is defined
as the number of imaging slices times the thickness of an imaging
slice. The image slice width is also called a scan slice. The
thickness of the imaging slice is defined by the thickness of the
slice in a rotation center position and desired value is selected
(e.g., from 0.5 mm, 1 mm, 2 mm, 3 mm and 4 mm). Thus, the number of
imaging slices is the number of detection element segments
corresponding to the thickness of the imaging slice (e.g., 0.5
mm).
There are a number of limitations associated with a conventional
multi-slice helical X-ray CT apparatus. For example, after the
operator sets that the number of imaging slices (e.g., =8) and a
helical pitch (e.g., =7), before imaging, the operator may change
the number of imaging slices (e.g., from 8 to 4) in response to
various demands (quality of image, imaging speed, etc.) changes. It
is possible in this case for an object to be imaged with the number
of slices=4 and the helical pitch remaining equal to 7 if the
operator forgets to change the helical pitch. As a result, an
artifact will appear on the reconstructed image. (Note helical
pitch is defined as the distance of the movement of the X-ray beam
along the rotation axis when it makes a turn around the patient
divided by the thickness of the imaging slice.) If the image many
such artifacts, it is necessary to re-image the patient and patient
throughput decreases.
SUMMARY OF THE INVENTION
It is an object of the present invention to supply a computed
tomography apparatus which assists the operator in easily and
correctly making an imaging plan.
One embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector configured to detect the
radiation from the object, a data collection unit configured to
collect projection data based on an output signal of the detector,
an input device configured to input an image slice width of the
object and a controller configured to select at least one of
reconstruction methods which can be used according to the inputted
image slice width and to control a display so as to display the
selected reconstruction method on a display.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector configured to detect the
radiation from the object, a data collection unit configured to
collect projection data based on an output signal of the detector
and a controller configured to control a display so as to display
at least one of reconstruction methods and its grade information on
a display.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector configured to detect the
radiation from the object, a data collection unit configured to
collect projection data based on an output signal of the detector,
an input device configured to input an image slice width of the
object, a controller configured to perform a priority processing or
an examination processing about typical feature of each
reconstruction method; and a reconstruction unit configured to
reconstruct an image of the object on the basis of the projection
data by the reconstruction method determined according to the image
slice width and a result of a priority processing or an examination
processing.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector configured to detect the
radiation from the object, a data collection unit configured to
collect projection data based on an output signal of the detector,
an input device configured to input the information related to an
imaging range of the object, a controller configured to select one
reconstruction method according to the inputted information and a
reconstruction unit configured to reconstruct an image of the
object on the basis of the projection data by the selected
reconstruction method.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector configured to detect the
radiation from the object, a data collection unit configured to
collect projection data based on an output signal of the detector,
a memory unit configured to store a plurality of reconstruction
methods, an input device configured to input the information
related to an imaging range of the object, a controller configured
to select at least one of reconstruction methods from the
reconstruction methods stored in the memory unit according to the
inputted information and to display the selected reconstruction
method on a display, a select device where an operator selects one
reconstruction method from at least one of reconstruction methods
displayed on the display and a reconstruction unit configured to
reconstruct an image of the object on the basis of the projection
data by the selected reconstruction method.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector including a plurality of
detection elements configured to detect the radiation from the
object, a data collection unit configured to collect projection
data based on an output signal of the detector, a mechanism
configured to move the detector to the object helically by a
helical pitch, an input device configured to change the number of
image slices of the object and a controller configured to change
the helical pitch according to the number of image slices.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector including a plurality of
detection elements configured to detect the radiation from the
object, a data collection unit configured to collect projection
data based on an output signal of the detector, an input device
configured to change the number of image slices of the object and a
controller configured to change a current of the radiation source
according to the number of image slices.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector including a plurality of
detection elements configured to detect the radiation from the
object, a data collection unit configured to collect projection
data based on an output signal of the detector, a mechanism
configured to move the detector to the object helically by a
helical pitch, an input device configured to change the number of
image slices of the object and a controller configured to give an
alarm in order to urge an operator to confirm the helical pitch
when the number of image slices is changed.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector including a plurality of
detection elements configured to detect the radiation from the
object, a data collection unit configured to collect projection
data based on an output signal of the detector, an input device
configured to change reconstruction thickness of an image of the
object, a controller configured to change image pitch according to
the changed reconstruction thickness and a reconstruction unit
configured to reconstruct the image of the object on the basis of
the projection data by the changed image pitch.
A further embodiment of the present invention includes a computed
tomography apparatus comprising a radiation source configured to
emit a radiation to an object, a detector including a plurality of
detection elements configured to detect the radiation from the
object, a data collection unit configured to collect projection
data based on an output signal of the detector, an input device
configured to change reconstruction thickness of an image of the
object and a controller configured to give an alarm in order to
urge an operator to confirm the image pitch when the reconstruction
thickness is changed.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same
becomes better understood by reference to the following detailed
description when considered in connection with the accompanying
drawings, wherein:
FIG. 1 is a block diagram showing an X-ray CT apparatus according
to the first embodiment of the present invention;
FIG. 2 is a plane view showing a detector module which an X-ray
detector includes;
FIG. 3 is a perspective view showing an X-ray detector, a switch
group and a data acquisition system (DAS);
FIG. 4 is an illustration of an example displayed on a monitor;
FIG. 5 is a flow chart explaining an operation of the first
creation mode in the first embodiment;
FIG. 6 is an illustration of an example displayed on a monitor in
the first creation mode;
FIG. 7 is a flow chart explaining an operation of the second
creation mode in the first embodiment;
FIGS. 8A and 8B is an illustration of an example displayed on a
monitor in the second creation mode;
FIG. 9 is a flow chart explaining an operation of the third
creation mode in the first embodiment;
FIG. 10 is a flow chart explaining an operation of a modified
creation mode for restricting one mode among three modes in the
first embodiment;
FIG. 11 is a flow chart explaining an operation of the second
embodiment;
FIG. 12 is a flow chart explaining an operation of the first
modification of the second embodiment;
FIG. 13 is an illustration of an example displayed on a monitor in
the second embodiment;
FIG. 14 is an illustration explaining an operation at the time of
scan;
FIG. 15 is an illustration of an example displayed on a monitor in
the first modification of the second embodiment;
FIG. 16 is an illustration of an example displayed on a monitor in
the first modification of the second embodiment;
FIG. 17 is an illustration explaining an operation at the time of
scan;
FIG. 18 is a flow chart explaining an operation of the second
modification of the second embodiment;
FIG. 19 is an illustration of an example displayed on a monitor in
the second modification of the second embodiment;
FIG. 20 is a flow chart explaining an operation of the third
modification of the second embodiment; and
FIG. 21 is an illustration of an example displayed on a monitor in
the third modification of the second embodiment.
DETAILED DESCRIPTION OF THE INVENTION
The first embodiment which is one example according to the present
invention will be explained reference to FIGS. 1 to 10. The first
embodiment is an example which selects automatically a
reconstruction method which can be used and displays it on the
basis of the information inputted by the operator. FIG. 1 is a
block diagram showing a multi-slice X-ray CT apparatus which is one
example of a computed tomography apparatus according to the first
embodiment. The multi-slice CT apparatus can perform not only a
multi-slice helical scan but also a conventional scan (single slice
scan or multi-slice scan).
The X-ray CT apparatus 100 has a bed where an object, such as a
patient, is laid, a gantry G which has an opening space OP and
collects projection data of the patient in it, and a data
processing unit U which controls the whole of the gantry G and
reconstructs an image from the projection data and displays it on a
monitor. The bed has a plate which can be slid in the longitudinal
direction by a bed control unit. Usually, the patient is laid so
that the body axis direction is along the longitudinal
direction.
The gantry G has an X-ray tube 101, as one example of a radiation
source, and an X-ray detector 103, as one example of a radiation
detector, arranged opposite the X-ray tube 101 such that the
patient P inserted in the opening space OP is positioned between
them. Furthermore, the gantry G includes a switch group 103a (refer
to FIG. 3), the data acquisition system (DAS) 104, a non-contacting
data communications unit 105, a gantry drive unit 107, and a slip
ring 108. The X-ray tube 101, the X-ray detector 103, and the data
acquisition system 104 are fixed in a rotation ring 102 which can
rotate within the gantry G. The rotation ring 102 rotates with the
X-ray tube 101, the X-ray detector 103, and the data acquisition
system 104 around a rotation center axis parallel to the body axis
of the patient P inserted into the opening space OP of a gantry G
by a gantry drive unit 107. The rotation ring 102 rotates at
high-speed speed, such as less than one second per rotation.
The X-ray tube 101 generates cone-beam (four-sided pyramid-like)
X-rays to the patient P laid in the field of view (FOV). An
electrical power (tube voltage, tube current) required for emitting
of the X-ray is supplied to the X-ray tube 101 through the slip
ring 108 from a high-voltage generating unit 109. Thereby, the
X-ray tube 101 generates the cone-beam which spreads in two
directions of a slice direction parallel to the above-mentioned
rotation center axis and a channel direction perpendicular to the
slice direction. In addition, between the X-ray tube 101 in gantry
G and the patient P, there is a collimator which forms the
appropriate size X-ray beam emitted from focus of the X-ray tube
101. The X-ray detector 103 is a device which detects the X-ray
which penetrated patient P and includes X-ray detection elements
arranged in the shape of an array in the two directions (the slice
direction and the channel direction). In the first embodiment, the
X-ray detector 103 has a plurality of detector modules (for
example, 38 pieces) arranged in the channel direction.
FIG. 2 is a plane view showing one detector module 1030. FIG. 3 is
a perspective view showing the 2-dimensional X-ray detector 103,
the switch group 103a and the DAS 104. The detector module 1030 has
a scintillator and a photo-diode tip which has a plurality of
detection elements 1031 and 1032 each of which includes a
photo-diode. The detection elements 1031 and 1032 are arranged in
the shape of a matrix in the two directions of the channel
direction and the slice direction. In addition, with the X-ray CT
apparatus in the first embodiment, the detector modules 1030 are
arranged in the array shape centering on the focus of the X-ray
tube 101 rather than in a flat shape. The detector module 1030 has
the above-mentioned photo-diode tips, switching tips included in
the switch group 103a, and a DAS tip included in the DAS 104. The
switch group 103a mounts switching elements, such as FET, for
example, on a switch board. The photo-diode tips, the switching
tips, and the DAS tips are mounted on a single rigid printed wired
board.
Moreover the detection element 1031 has the sensitivity area where
the X-ray can be detected. The width of the sensitivity area of the
detection element 1031 is 1.0 mm in the slice direction and 0.5 mm
in the channel direction. While, the width of the sensitivity area
of the detection element 1032 is 0.5 mm in the slice direction and
0.5 mm in the channel direction. The width of the sensitivity area
is defined as the width on the rotation center axis. That is to
say, "the photo-diode has 1 mm sensitivity area" means "the
photo-diode has the sensitivity are which is equivalent to 1 mm on
the rotation center axis of the X-ray tube." As the X-ray spreads
in the shape of radiation, the width of actual sensitivity on the
photo-diode is larger a little than 1 mm according to both of the
distance between the X-ray focus and the rotation center axis and
the distance between the X-ray focus and the photo-diode. As shown
in FIG. 2, sixteen detection elements 1032 of 0.5 mm width are put
in the slice direction, for example. A group of the sixteen
detection elements 1032 is called hereinafter the first detection
elements segment. Moreover, on both sides of the first detection
elements segment in the slice direction, there are twelve detection
elements 1031, for example, of 1 mm width than the number of the
detection elements 1032. Each group of the twelve detection
elements 1031 put in the slice direction is called hereinafter the
second detection elements segment. In the first embodiment, the
X-ray detector is designed such that the number (for example, 16
elements) of the detection elements 1032 put in the slice direction
is more than each number (for example, 12 elements) of the
detection elements 1031 arranged at each side, and is less than the
total number (for example, 24 elements) of the detection elements
1031. That is, in the first embodiment, there are 912 detection
elements in the channel direction (line direction) and 40 detection
elements in the slice direction (segment direction). In addition,
although the X-ray detector 103 in the first embodiment has the
2-dimensional detector including unequal width detection elements
that are the 0.5 mm detection elements and the 1.0 mm detection
elements, a 2-dimensional detector which has equal width detection
elements may be used. Furthermore, the size of the detection
element is not limited to the first embodiment, such as 0.5 mm and
not 1.0 mm but 1.25 mm width, for example.
The DAS 104 which has data collection elements, such as 912 lines
times 8 segments or 912 lines times 4 segments. The number of the
data collection elements is fewer than that of the detection
elements, such as 912 lines times 40 segments. The detected data is
sent to the switch group 103a which adds the data in the slice
direction in the control of a host controller 110, and transmitted
to the DAS 104. The projection data outputted from the DAS 104 is
transmitted to the below-mentioned a data processing unit U through
the non-contacting data communications unit 105 which uses an
optical communication device. The slip ring may be used for the
data communication instead of the optical communication device. The
data collection repeats at high speed, such as about 1000 times per
a rotation.
In the DAS 104, it is determined according to the reconstruction
method, the fan-beam reconstruction method or the cone-beam
reconstruction method, in a imaging plan as described below,
whether eight data collection elements or four data collection
elements. That is to say, the number of data collection elements
used depends on the reconstruction method. In the first embodiment,
when performing the fan-beam reconstruction method (for example, 2
mm and 4 slices etc.), four data collection elements (for example,
912 lines and 4 segments) are used, while, when performing the
cone-beam reconstruction method (for example, 0.5 mm and 8 slices
etc.), eight data collection elements (for example, 912 lines and 8
segments) are used.
The data processing unit U has mainly the host controller 110, a
pre-processing unit 106 which pre-processes the projection data,
such as data compensation, a memory unit 111, a subsidiary memory
unit 112, a main data processing unit 113, a reconstruction unit
114, an input unit 115, and a display 116 which are mutually
connected through a data control bus 116. Furthermore, the data
control bus 116 is connected to an external image processing unit
200. The image processing unit 200 includes a subsidiary memory
unit 201, a main data processing unit 202, a reconstruction unit
203, an input unit 204, and a display 205.
The pre-processing unit 106 performs the sensitivity compensation
or X-ray strength compensation, etc. of the projection data
transmitted from the non-contacting data communications unit 105.
360 degrees, 1000 sets of the 2-dimensional projection data
performed the sensitivity compensation or the X-ray strength
compensation with the pre-processing unit 106 are once stored in
the memory unit 111. Moreover, an imaging planning program which is
a program for carrying out the above-mentioned imaging plan is
stored in the subsidiary memory unit 112. The reconstruction unit
114 reconstructs slice image data on the basis of the projection
data stored in the memory unit 111 by the fan-beam reconstruction
method or the cone-beam reconstruction method. The cone-beam
reconstruction method uses algorithm called Feldkamp method. The
Feldkamp method is approximate reconstruction method improved on
the basis of the fan-beam convolution back projection method in
order to treat the wide range in the slice direction as a group of
a plurality of box data cells and to make the 3-dimensional
distribution data (hereinafter called volume data which a plurality
of data cells are gathered 3-dimensionally)) of an X-ray absorption
coefficient. That is, in the Feldkamp reconstruction method, the
projection data is convoluted as the fan projection data, and the
convoluted data is back-projected along with a slant ray according
to the actual cone angle to the rotation center axis.
Furthermore, if one or more of the following compensation processes
are performed in reconstruction process by the cone-beam
reconstruction method, the error of reconstruction can be reduced.
The first compensation process compensates the error caused by the
reason that the X-ray beam passes long inside of the patient long
since the X-ray beam is aslant. That is, it compensates the
projection data (the pre-processing may not be performed) for the
difference length according to the position in the slice
direction.
The second compensation process compensates the error caused by the
reason that the actual X-ray path is different from the calculated
path between the X-ray focus and the center of the box data cell in
the reconstruction process.
That is, the projection data detected along with a plurality of the
actual X-ray paths near the calculated paths is changed to the
back-projection data along with the calculated path. The
back-projection data is weighted and back-projected. Especially in
the helical scan, since the position between the X-ray focus and
the reconstructed slice changes in the slice direction, it is
desirable to change the weight of the data according to the
position. In the above-mentioned cone-beam reconstruction method, a
large detector in the slice direction is effectively used. In
addition, another algorithm of this cone-beam reconstruction method
using the cone angle information like ASSR method described in
Japanese patent publication No. 8-187240 may be used, for example.
The ASSR method is that the approximation projection data on the
X-ray path approximated to the position of the virtual plane (being
set up as a slanting plane which inclines to the center axis of the
helical scan is more effective) obtained from 2-dimensional
projection data is extracted.
While, the fan-beam reconstruction method uses the fan-beam back
projection method, as described in Japanese patent publication No.
10-248837, where the image is reconstructed as the X-ray is
perpendicular to the rotation center axis (the projection data is
assumed to be obtained by the X-ray perpendicular to the body axis
direction). In the fan-beam reconstruction method, the main data
processing unit 113 performs a helical compensation to the
projection data. In the helical compensation, projection data (360
degrees projection data or 180 degrees+fan angle data) is obtained
by a line-compensation of the same phase projection data near the
slice. In the first embodiment, the helical compensation is
improved. The main data collection unit 113 pre-sets re-sampling
points of a predetermined number in the predetermined range near
the slice, obtains the re-sampling data by inter-compensating at
the re-sampling points, and makes the projection data of the slice
by weighting the re-sampling data with a filter. The reconstruction
unit 114 generates the image from the projection data by the
fan-beam reconstruction method. While, in the cone-beam
reconstruction method, the above-mentioned first and second
compensations are used instead of the helical compensation.
The reconstructed volume data is directly or once stored in the
memory unit 111, transmitted to the data processing unit 113. The
volume data is changed to the image, such as a slice image, a
sectional image and a so-called 3-dimensional image data which is a
3-dimensional surface image of the specific organs by rendering
processing. The image is displayed on the display 116.
The operator can select the image among the above-mentioned images
according to the purpose of inspection and diagnosis. In this case,
the image is generated and displayed in a different form from the
same volume data. Moreover, the operator can select the first mode
where one image selected is displayed or the second mode where a
plurality of the images are displayed simultaneously according to
the purpose.
The host controller 110 controls each unit as described below and
collects the X-ray penetration data (projection data). Namely, the
host controller 110 stores in an internal memory the scanning
conditions, such as slice thick, inputted through the input unit
115 by the operator. On the basis of the stored or inputted
directly scanning conditions, the high-voltage generating unit 109,
a bed drive unit, and the gantry drive unit 107 are controlled. In
detail, the amount of sliding of the bed to the body axis
direction, the sliding speed, the rotation speed of the gantry (the
X-ray tube 2014 and the detector 103), a rotation pitch and the
timing of the X-ray, etc. are controlled. Thereby, the cone X-ray
beam is emitted to the field of view of the patient from many
directions, the penetrated X-ray is detected by each detection
element of the detector 103. The host controller 110 controls
ON/OFF of the switching elements of the switch group 103a according
to the scanning conditions (especially image slice width (the
number of imaging slices times the thickness of the imaging slice))
set up with the input unit 115. Thereby, addition of the signals
between the segments is performed before DAS by which the
connection between the detection elements (photo-diodes) of the
X-ray detector 103 and the data collection elements of the DAS 104
is changed according to the thickness of the imaging slice. In
addition, according to the thickness of the imaging slice, the
collection data of DAS 104 can also be added by processing, which
is called addition after DAS. The processing of the addition can be
performed with the pre-processing unit 106.
Moreover, in addition to control of the connection state of switch
group 103a mentioned above, the host controller 110 switches the
number (for example, four segments for the fan-beam reconstruction
method or eight segments for the cone-beam reconstruction method)
of the DAS segments in the slice direction used for the data
collection. The X-ray projection data of a plurality of slices
corresponding to the scanning conditions or the reconstruction
conditions is outputted from the DAS 104. Among the data processing
unit U mentioned above, the host controller 110, the input
apparatus 115 and the display 116 are an interactive interface
between the apparatus and the operator. The interactive interface
is used as an imaging planning creation system 120 when the
operator makes the imaging plan before actual scan according to the
imaging planning program stored in the subsidiary memory unit
112.
The imaging planning creation function of the imaging planning
creation system 120 includes the input and set of many conditions,
such as FOV, the flow from the scan to the record, the scanning
conditions, the reconstruction conditions, and the image
display/record conditions.
Generally, the set of the scanning conditions, such as tube
voltage, tube current, and the timing of the X-ray, and the
reconstruction conditions, such as the image slice width (the
thickness of the imaging slice times the number of slices) and
matrix size, needs special knowledge. Since the function is based
on the special knowledge, even a novice operator can make an
equivalent imaging plan.
As the flow from the scan to the record, there is a flow of
conventional scan which repeats the bed movement after the scan
during the bed stop. Additionally, with the conventional scan,
there are scan-scan mode which reconstructs and displays images
after the scan of the total slices is completed and scan-view mode
which repeats the scan by the reconstruction/display of the image
in each position.
While, as the flow of the helical scan, there are auto filming mode
which performs the fan-beam reconstruction or the cone-beam
reconstruction following the helical scan and makes films according
to the predetermined window conditions while displaying images on
the display, active auto filming mode which enables the operator to
adjust the window conditions, if necessary, during the scan and
suspends filming during adjustment of the window conditions, and
real time mode which performs a real time reconstruction following
the helical scan and makes films of the image obtained by the
fan-beam reconstruction or the cone-beam reconstruction which
different from the real time scan.
The helical scan (called corkscrew scan or spiral scan) moves the
patient, rotating the source of the X-ray continuously in the case
of the third generation or the forth generation type of the X-ray
CT apparatus. In this helical scan, the position of the patient
changes continuously during emission of the X-ray according to the
rotation angle of the source of the X-ray. That is, the position of
the scanning plane to the patient changes continuously.
A plurality of parameters are concerned with collection operation
(scanning operation) of the projection data. A plurality of
parameters are concerned also with reconstruction operation which
reconstructs images on the basis of the collection signals and
image display operation which displays images, respectively.
As the scanning conditions (signal collection parameters), there
are an imaging part of the patient (a whole body, a head, a chest,
a lung, a leg, etc.), a scan type (conventional scan (multi-slice
scan or single slice scan) and helical scan), the thickness of the
imaging slice, a slice interval, the number of the slices used for
the multi-slice scan, volume size, the tilt angle of the gantry,
tube voltage, tube current, the size of FOV, scanning speed
(rotation speed of the X-ray tube and the detector) and the
distance of the bed movement while the X-ray tube and the X-ray
detector rotates around the patient once, for example. While, as
the reconstruction conditions, there are the reconstruction method
(the fan-beam reconstruction method or the cone-beam reconstruction
method), a reconstruction thickness of the image, the pitch between
images (image generation pitch), reconstruction size,
reconstruction matrix size, and a threshold which extracts an
interested part, for example. Furthermore, as image display/record
conditions (image display/record parameter), there are a window
level, window width, display magnification, and multi-planer
(sagittal, coronal, oblique, etc).
In this first embodiment, when the operator sets the reconstruction
method (the fan-beam reconstruction method or the cone-beam
reconstruction method), effective reference information for the
setting of the reconstruction method can be displayed, or the
reconstruction method can be automatically selected according to
the required information inputted by the operator since the
operator can communicate the apparatus interactively with the input
unit 115. For this, the first to third creation modes are prepared
as shown in FIGS. 5 to 10.
In order to complete the imaging sequence from the signal
collection to the image display through the image reconstruction,
it is required that the scanning conditions mentioned above,
reconstruction conditions, and image display/record conditions are
set up, respectively. The flow to set these conditions
(parameters), such as the signal collection, the reconstruction,
the image display/record is called a plan. The operator makes the
plan where the scanning conditions, the reconstruction conditions,
and the image display/record conditions can be included in order to
make it convenient. By choosing the plan, a series of
above-mentioned whole conditions can be set easily. Under support
of the imaging planning creation system 120, the operator sets up
the imaging plan (schedule). According to the set-up schedule, the
host controller 110 controls the gantry and the bed to perform the
schedule one by one.
One example displayed on a monitor when setting the imaging plan is
shown in FIG. 4. In this figure, a screen for setting up the
scanning conditions is shown. This schedule setting screen is
displayed on the monitor of the display 116, however it may be
displayed on a monitoring screen of the input unit 115. A scanogram
image (SN), created based on the data obtained by moving bed when
the X-ray tube and the X-ray detector are not moved, is displayed
on the upper right position of this schedule setting screen. A
frame for setting up the scanning range on this scanogram image is
also displayed. The operator can set all scanning areas (all
scanning ranges) by reducing, moving, expanding and rotating the
frame. The object (patient) information is displayed on the upper
and central part of this schedule setting screen, and a process
after the data collection is further displayed on its left.
Furthermore, various kinds of buttons which the operator operates
if necessary are displayed under the patient information and the
process. There are B1 to B5 buttons for priority instructions of
the amount of the emitted X-ray to the patient (X-ray dose),
scanning time, the total time of scan and reconstruction, quality
of image, and X-ray tube OLP (Over Load Protection of the X-ray
tube), respectively, and a button C used for confirmation of the
operator's intention. Furthermore, a scanning schedule table is
displayed at the bottom of this setting screen.
In this scanning schedule table, a plurality of scanning operations
are perpendicularly arranged according to the order of a series.
The operator makes and arranges using each function, such as a new
addition, a copy, and an elimination. In each column, the start
time of each scanning operation on the basis of the time when the
operator pushes a trigger button, the pause time between scanning
operations, the scan start position, the scan stop position, the
scan type (the conventional scan (multi-slice scan, single-slice
scan)/the helical scan), the helical pitch, and the main buttons
are arranged. The main buttons indicates buttons for the number of
times of scanning, the tube voltage supplied to the X-ray tube 101
from the high-voltage generating unit, the tube current, the
scanning speed (scanning total time), the size of FOV, the image
slice width (the thickness of the imaging slice times the number of
slices), the scanning range, the amount of movements of the bed
after the scan, respectively.
By clicking the button of a reconstruction parameter, as
reconstruction conditions, the imaging planning creation system 120
displays the reconstruction method (the fan-beam reconstruction
method/the cone-beam reconstruction method), the thickness
(reconstruction thickness) of a reconstruction slice, the image
generation pitch, the reconstruction size, the reconstruction
matrix size, and a threshold which extracts an interested part, for
example. Initial recommendation value of each condition is inserted
by the imaging planning creation system 120, and the operator can
change the value if needed. In addition, the size or the position
of the flame on the scanogram image changes automatically when the
value of the start position, the stop position, the scanning range,
or the size of FOV is changed. If the flame is moved by clicking
each value is changed.
Next, the operation of the X-ray CT apparatus in the first
embodiment will be explained. The following operation is performed
by the operator based on the imaging planning program stored in the
subsidiary memory unit 112. The operator inputs information, such
as the process after the data collection and the patient
information on the screen of the display of the input unit 115
shown in FIG. 4. The operator takes the scanogram image data of the
patient by generating the X-ray from the X-ray tube without
rotating the X-ray tube and the detector and inserting the bed into
the opening space of the gantry. By processing the scanogram image
data obtained as described above, the scanogram image can be
obtained. This scanogram image SN is described as shown in FIG. 4
on the screen. In FIG. 4, the case where the operator selects the
auto filming mode is shown.
Next, the operator sets the flow from the scan to display/record,
such as the imaging part of the patient, the scan conditions, the
reconstruction conditions, the display/record conditions (window
conditions) etc. on the screen according the imaging planning
program. The imaging planning creation system 120 prepares the
first to third modes in order that the operator can set the
conditions easily.
The first creation mode is shown in FIGS. 5 and 6. This first
creation mode aims at showing the operator the candidate of a
possible reconstruction method. The operator finally determines the
reconstruction method with its intention with reference to the
shown reconstruction method. Specifically, the imaging planning
creation system 120 reads the image slice width inputted by the
operator (Step 1). The imaging planning creation system 120
determines the candidate of a reconstruction method applicable to
the image slice width with reference to the look-up table stored
beforehand (Step 2). Thereby, the candidate of one or more
reconstruction methods is determined and shown to the operator
(presentation). The fan-beam reconstruction method (additional
processing before DAS or after DAS is also included) and/or the
cone-beam reconstruction method are included in the candidate of
these reconstruction methods.
Next, the detailed parameter contained in each determined
reconstruction method is calculated in the imaging planning
creation system 120 (Step 3). Thus, the reconstruction method and
the calculated parameter are displayed (presented) in the imposed
mode on the screen, as shown in FIG. 6 (Step 4). According to the
image slice width, two kinds of reconstruction methods are listed
on this imposed screen, for example. In FIG. 6, as the
reconstruction methods the fan-beam reconstruction method
(additional processing before DAS or after DAS is also included),
and the cone-beam reconstruction method are displayed. Each
reconstruction method is subdivided according to the kind of
applicable scan types (multi-slice scan, helical scan, etc.). The
parameter is displayed for every classification decided by
combination of the reconstruction method and the scan types.
In this parameter, the information showing the Feldkamp
reconstruction or ASSR reconstruction when the reconstruction
method is the cone-beam reconstruction method, and the information
showing the helical compensation method when the helical scan is
used are also included. Thereby, a series of flow of the
multi-slice helical scan, additional processing method before DAS
or after DAS, the helical compensation method, the fan-beam
reconstruction method (the number of slices is four) is shown.
Another series of flow of the multi-slice conventional scan, the
length compensation, the cone-beam reconstruction method is
displayed. A check button for the operator choosing is displayed on
the tail end of each flow of the presentation screen,
respectively.
The operator who takes a look at the presentation screen of this
reconstruction method chooses a desired combination of the
reconstruction method and the scan type by clicking the check
button. The imaging planning creation system 120 detects whether
the button is clicked or not (Step 5). When it determines NO,
namely it is not clicked, it determines whether a setup of the
reconstruction method is cancelled or not on the basis of another
operation information (Step 6). If it is also NO, the imaging
planning creation system 120 recognizes that the operator keeps
consideration, then returns the processing of Step 5. While, the
judgment of Step 6 is YES, since it is recognized to be cancelled
and it ends processing. In Step 5, if it detects YES, since it
means one of combinations of the reconstruction method and the scan
type is chosen, the selected reconstruction method is memorized in
the memory unit 111, and the processing is ended (Step 7).
The second creation mode is shown in FIGS. 7, 8A and 8B. The second
creation mode presents the grade information on each reconstruction
method in addition to the reconstruction method shown in the first
creation mode mentioned above. The only grade information may be
displayed. In order to show this grade information, the imaging
planning creation system 120 performs the processing shown in FIG.
7. This processing adds step 3A and 4A to the processing of FIG. 5
in the first embodiment.
In step 3A, the grade information on a reconstruction method is
read from the grade information table stored beforehand according
to one or more reconstruction methods determined at Step 2. This
read grade information is imposed on the screen in list form as
shown in FIGS. 8A and 8B (Step 4A). The grade information in FIGS.
8A and 8B is evaluated in the cases of the fan-beam reconstruction
method (the number of slices is four) and the cone-beam
reconstruction method (the number of slices is eight) by each item,
such as the X-ray dose, the scanning time, the total time from the
scan to the reconstruction, quality of image (low contrast/high
contrast), and X-ray tube OLP (scanning waiting time). In FIGS. 8A
and 8B, the character of "E" shows excellent in comparison with the
other reconstruction method, and the character of "B" shows bad
vice versa. Instead of E or B, other marks, such as circle mark,
triangle mark, and X mark.
The X-ray dose is related to the size of the imaging where data is
collected. When the image slice width is thick, the cone-beam
reconstruction method is better (the X-ray dose is low) than the
fan-beam reconstruction method. While, the fan-beam reconstruction
method is better (the X-ray dose is low) than the cone-beam
reconstruction method, if the image slice width is thin. With
regard to the scanning time, since the detector includes many
detection segments, the cone-beam reconstruction method is better
(short) than the fan-beam reconstruction method, generally. On the
other hand, about the total time from the scan to the
reconstruction, the fan-beam reconstruction method is better than
the cone-beam reconstruction method, when image slice width is
thick. About the quality of image, the cone-beam reconstruction
method is better, and about the X-ray tube OLP, the cone-beam
reconstruction method is better.
As described above, in the second creation mode, in addition to
presentation of one or more reconstruction methods, the grade
information is shown by item showing the typical feature of each
reconstruction method. In addition, if the only grade information
is shown, Steps 3 and 4 are removed among the steps in FIG. 7.
Thus, in the first and second creation modes, according to the
image slice width which the operator gives on the imaging planning
creation screen, the candidate of the reconstruction methods and
its parameter information, and/or the grade information on each
reconstruction method are shown automatically. Since important
information for the determination of the reconstruction method is
immediately acquired on the screen, it becomes easy for the
operator to decide the suitable reconstruction method. Therefore,
even a novice operator can make an excellent imaging plan, the time
for it can be vastly shortened, and the operation of the operator
can be efficient. In addition, the burden on the operator is
reduced, and the patient processing efficiency is improved. Thus,
setting mistake of the imaging plan etc. can be prevented and the
accurate and reliable imaging plan can be created.
Next, the third creation mode will be explained with reference to
FIG. 9. As for the third creation mode, the imaging planning
creation system 120 sets up the scan type and the reconstruction
method automatically. The imaging planning creation system 120
performs a series of processing shown in FIG. 9. The imaging
planning creation system 120 reads the image slice width set by the
operator (Step 11). The imaging planning creation system 120 judges
whether "priority processing" or "examination processing" is
performed based on operation information from the operator (Step
12). Here, the "priority processing" is processing which sets the
reconstruction method according to the order of priority among
items which shows the typical feature of each reconstruction
method, such as the X-ray dose, the scanning time, the total time
from the scan to the reconstruction, quality of image (low
contrast/high contrast), and one or more of the X-ray tube OLP
(scanning waiting time). This ordering is set by the operator. The
"examination processing" is processing which sets the
reconstruction method according to the instructions from the
operator about the above-mentioned items, such as the scanning
time, the total time, quality of image, and the X-ray tube OLP.
If the priority processing is selected by the operator at step 12,
the imaging planning creation system 120 sets the first priority
(for example, the X-ray dose), the second priority (for example,
the scanning time), the third priority (for example, the total
time), and the forth priority (for example, quality of image)
through Steps S13 to S16 according to the input from the operator.
In this case, the X-ray tube OLP remains (set as the fifth
priority). Only the first priority may be made or the first to the
third priority may be set, as another example.
After the priority is set, the imaging planning creation system 120
searches the stored reference table according to the priority
information, sets the optimum scan type and the reconstruction
method (Step 17). On the other hand, when the "examination
processing" is selected by the operator at Step 12, the imaging
planning creation system 120 shifts to Step 18, and chooses at
least one of examination items (for example, the scanning time)
according to the input from the operator. Also in this case, the
imaging planning creation system searches the reference table
according to the examination information, and determines the
optimum scan type and the reconstruction method (Step 19). The scan
type and the reconstruction method according to the image slice
width are displayed, for example imposed, on the imaging planning
creation screen (Step 20). The information on this scan type and
the reconstruction method are stored in the memory unit 111 (Step
21).
Thus, in the third creation mode, since the optimum scan type and
reconstruction method are set automatically according to the image
slice width the operator inputs, the burden on the operator can be
reduced. Moreover, failure of making the imaging plan is also
prevented, even if a novice operator makes it.
The imaging plan is interactively formed between the imaging
planning creation system 120 and the operator through the set of
the above scan type and the reconstruction method. Two or more
parameters related with the selected imaging plan, such as the
signal collection, image creation, and the image display are loaded
to the host controller 110. After the operator orders the imaging
start, the signals are collected according to the loaded the signal
collection parameter, the image is reconstructed according to the
loaded the reconstruction parameter, the image is displayed or
recorded according to the loaded image display or record parameter,
and the image is filmed according to the loaded window
conditions.
Moreover, a modification of the above-mentioned first to third
creation modes is shown in FIG. 10. Although the creation mode can
be selected by the operator in the above-mentioned embodiment, in
this modification, the creation mode can be restricted to one. In
this modification, at the time of installation of the multi-slice
X-ray CT apparatus, the one creation mode to use is decided, and a
serviceman restricts other creation modes in the memory unit 111
(the first to third creation modes are installed in advance) (FIG.
10, Steps 31 and 32).
Thus, the same X-ray CT apparatus can be used in different ways,
the second creation mode in Japan and the third creation in the
U.S., for example. In addition, the image slice width can be set up
in consideration of the limit of the image slice width by which a
cone angle influences quality of image. The number (the number of
segments of DAS) of slices can be changed to not only in four but
also suitable number like one or two in the fan-beam reconstruction
method, and can be changed to not only eight but also other number,
16, 32, or 64, for example. In addition, the DAS 104 uses two
segments in the fan-beam reconstruction method, and four segments
can be used in the cone-beam reconstruction method.
The present invention is not limited to the above embodiment, and
various modifications may be made without departing from the spirit
or scope of the general inventive concept. For example, although
the number of segments of the DAS in the body axis direction is
switched to eight segments or four segments etc. according to the
reconstruction algorithm or the image slice width in the above
embodiment, the number of the segments may be fixed to a
predetermined number (for example, eight segments). In this case,
the number of slices can be selected, four or eight, for example,
in a reconstruction parameter sheet. Thereby, the operator can save
the time to choose the number of slices of scanning conditions in
the imaging plan.
Moreover, in the above-mentioned embodiment, although the X-ray CT
apparatus 100 itself executes data processing like the
reconstruction processing, cross-sectional conversion processing
and display processing, instead of this, the external image
processing unit 200 shown in FIG. 1 may performs the processing. In
this case, the data may be transmitted from the X-ray CT apparatus
100 to the external image processing unit 200, before the
reconstruction, after the reconstruction or just before the
display.
Moreover, in the above-mentioned embodiment, although ROTATE/ROTATE
type where an X-ray tube and a detector rotate around the patient
is explained, (STATIONARY/ROTATE) type where the array of many
detection elements are arranged as the shape of a ring and the only
an X-ray tube rotates around the patient may be used. Moreover,
although the case where the about 360 degrees projection data
around the patient is used for the reconstruction is explained in
the above embodiment, any reconstruction algorithm like a half scan
where 180 degree and view angle projection data may be used.
Furthermore, although the above-mentioned embodiment explains the
indirect conversion type detector where the X-ray changes into the
light with the scintillator and the light is converted to into an
electric charge with light-electronic conversion elements, such as
a photo-diode, the direct type detector where the X-ray directly
changes to an electric charge with the semiconductor material where
the electron hole pair is generated and moves each side may be
used. Moreover, in the above-mentioned embodiment, although one
X-ray tube type X-ray CT apparatus is explained, two or more pairs
of an X-ray tube and an X-ray detector, so-called multi X-ray tube
type X-ray CT apparatus may be used.
As explained above, even the operator who is not skilled can set
the appropriate reconstruction method easily, and the imaging plan
can be made easily and quickly without the much burden of the
operator.
Next, the second embodiment according to the present invention is
explained with reference to FIGS. 11 to 21. Although, in the first
embodiment, especially the reconstruction method is explained, the
second embodiment is related with the helical pitch, etc. of the
multi-slice CT apparatus. The second embodiment is different from
the first embodiment in the imaging planning program stored in the
subsidiary memory unit 112.
In the first example according to the second embodiment, the
helical pitch, etc. is automatically displayed on the basis of the
information inputted by the operator. The operation of this first
example is explained. The operator inputs predetermined
information, such as the patient information and the process
information after the data collection, on the imaging planning
creation screen, shown in FIG. 4, displayed on the display 116 of
imaging planning creation system 120. Subsequently, the operator
takes a scanogram image data of the patient. Predetermined
processing is performed to the scanogram image data, and the
scanogram image SN is obtained. This scanogram image SN is
displayed as shown in FIG. 4 on the imaging planning creation
screen. In FIG. 4, the case where the operator selects the auto
filming mode is shown. Next, the operator sets the flow from the
scan to the display/record, such as the imaging part of the
patient, the scan conditions, the reconstruction conditions, the
display/record conditions (window conditions) etc. on the screen
according the imaging planning program. In this case, the assistant
processing shown in FIGS. 11 and 12 automatically executed by the
X-ray CT apparatus. The assistant process starts according to the
start of the imaging planning process (main process) and runs in
the background of the imaging planning process by the host
controller 110 which is the central part of the imaging planning
creation system 120. Therefore, the operator can be assisted and
concentrate on making the imaging plan without considering such
assistant process. FIG. 11 shows the assistant process when the
number of the used segments of the X-ray detector 103, namely the
number of slices, is changed in the middle of the imaging planning
creation processing mentioned above. In detail, the host controller
110 reads the number (the number of detector element segments) of
slices specified, the helical pitch, and the tube current (Steps 1
to 3). The host controller 110 judges whether the number of slices
is changed in the imaging planning creation processing (Step 4).
Since the host controller 110 watches the inputted value to the
window (refer to FIG. 4) of the image slice width on the imaging
planning creation screen with the input unit 115, the
above-mentioned change can be checked based on the change of this
value.
When it is judged YES which means the number of the slices is
changed in Step 4, the host controller 110 calculates the
appropriate helical pitch according to the number of change slices
(Step 5). The calculated helical pitch may be proportionate to the
number of the changed slices, may be proportionate and approximate
to the changed number, or may be proportionate to the changed
number and shifted to the high-density sampling by 0.5 pitches. For
example, in the case of proportion, if the operator changes the
slice number (the number of detection segments) to 8 after it is
set that the slice number is 4 and the helical pitch is 5, the
helical pitch is automatically changed into 10. In addition, after
the slice number is set 8 and the helical pitch is 7, the slice
number changes into 4, then the helical pitch is automatically
changed to 3.5.
The host controller 110 calculates the tube current supplied to
X-ray tube 101 according to the number of changed slices (Step 6).
For example, after it is set the slice number is 4 and the helical
pitch is 5, if the slice number is changed to 8, the tube current
is automatically changed into a half. Thereby, the X-ray dose is
kept equivalent. The host controller 110 updates the helical pitch
and the tube current calculated at Steps 5 and 6 on the display and
stores them (Step 7). Furthermore, the updated information is
automatically displayed (Step 8), for example, the updated helical
pitch and the tube current may be blinked for a predetermined
period of time or the message indicates the change may be
displayed. Then, the host controller 110 waits for a predetermined
period of time, and it detects the next processing timing, and the
step is back to the Step 4 unless it is ordered in an end of
processing (Steps 9 and 10).
Although both of the helical pitch and the tube current are changed
automatically in processing of FIG. 11 as mentioned above, only one
of them may be performed. As one example where the only helical
pitch is changed, after it is set that the slice number is set 8
and the helical pitch is 7, the slice number changes into 4. In
this case, the helical pitch is automatically changed into 3.5
which is half value by processing of FIG. 11 mentioned above. After
the operator confirms this change, the updated value is used for
the scan. The state of the X-ray after changing is shown in FIG.
14.
As one example where the only tube current is changed, after it is
set that the slice number is set 4 and the helical pitch is 5, the
slice number changes into 8. In this case, the tube current is
automatically changed from 120 mA to 60 mA which is half value by
processing of FIG. 11. In this case, the helical pitch keeps 5.
Next the case where the reconstruction thickness is changed is
explained with reference to FIG. 12. The host controller 110 reads
the reconstruction thickness of the imaging slice and the image
pitch (Steps 11 and 12). The host controller 110 judges whether the
reconstruction thickness is changed in the imaging planning process
(Step 13). Since the host controller 110 watches the inputted value
to the window (refer to FIG. 15) of the reconstruction thickness on
the imaging planning creation screen with the input unit 115, the
above-mentioned change can be checked based on the change of this
value.
When it is judged YES which means the reconstruction thickness is
changed in Step 13, the host controller 110 calculates the
appropriate image pitch according to the reconstruction thickness
(Step 14). In this calculation, the image pitch which is
proportionate to the changed reconstruction thickness is obtained.
For example, although the reconstruction thickness is set 1 mm and
the image pitch is 1 mm once, the reconstruction thickness is
changed to 0.5 mm, then the image pitch is automatically changed
into 0.5 mm. The host controller 110 updates the reconstruction
thickness calculated at Steps 14 on the display and stores it (Step
15). Furthermore, the updated information is automatically
displayed (Step 16), for example, the updated reconstruction
thickness may be blinked for a predetermined period of time or the
message indicates the change may be displayed.
Then, the host controller 110 waits for a predetermined period of
time, and it detects the next processing timing, and the step is
back to the Step 13 unless it is ordered in an end of processing
(Steps 17 and 18). As one example, although the reconstruction
thickness is set 1 mm and the image pitch is 1 mm once, the
reconstruction thickness is changed to 0.5 mm, then the image pitch
is automatically changed into 0.5 mm. In this case, the displayed
image pitch on the imaging planning creation screen is changed from
FIG. 15 to FIG. 16. After the operator confirms this change, the
updated value is used for the scan. The state of image pitch and
the reconstruction thickness are shown in FIG. 17. Thus, even if
the reconstruction thickness is changed, images can be
reconstructed with no gaps. In the above-mentioned example,
although it is set that reconstruction thickness is 1 mm and the
image pitch is 1 mm,the thickness can be changed to 2 mm. In this
case, the image pitch is also automatically changed into 2 mm.
As mentioned above, in the first example of the second embodiment,
when making the imaging plan with the using the multi-slice helical
CT apparatus, even if the number of the slices or the image
thickness is changed, the parameter which relates to the number of
slices or the image thickness (the helical pitch, the tube current
and the image pitch) can be automatically changed.
Therefore, since it can prevent the operator from missing changing
the parameter, and also from obtaining the low quality of image
because of the missing. Moreover, since the re-imaging due to such
a cause is not necessary, the X-ray dose can be reduced.
Furthermore, since the operator may not watch and change the
related parameter manually, the burden of the operator can be
reduced and the patient throughput can be improved.
The second example of the second embodiment will be explained with
reference to FIGS. 18 and 19. In the following explanation, the
same mark is used for a thing the same as that of the first
embodiment, and the explanation is omitted or simplified. FIG. 18
shows the alert (warning) processing at the time of changing of the
number of the detector element segments, namely the number of
slices, of the X-ray detector 103 in the middle of the imaging
planning creation processing mentioned above. Specifically, the
host controller 110 performs Steps 21 to 24 which are the same
processing as Steps 1 to 4 in FIG. 11 mentioned above. In Step 24,
if it is judged that the number of slices is changed into another
value, the host controller 110 displays, on the imaging planning
creation screen, the alert (warning) information which urges the
operator to confirm the value of the helical pitch and/or the tube
current that are relevant to the number of slices (Step 25).
This warning is performed in various kinds of modes, such as
changing the background color of the window of the helical pitch
and/or the tube current, blinking the value of the helical pitch
and/or the tube current, generating a sound with it, and displaying
a pop-up message, as shown in FIG. 19. The example shown in this
FIG. 19 shows that the number of slices is set 8 and the helical
pitch is set 7 at the beginning for the helical scan, but the
operator changes the number of slices to 4, then the background
color of the window of the helical pitch and/or the tube current is
changed into a conspicuous color in order to urge the operator to
check the changed. After the alert, the host controller 110 judges
whether the value of the helical pitch and/or the tube current is
changed by the operator or not (Step 26). Subsequently, in a
certain period of time, if such value is changed, the host
controller 110 judges the value is appropriate or not with
reference to a table, for example (Step 27).
If the value is appropriate, it stands by to next processing
timing, and processing is returned to Step 24 (Steps 28 and 29). On
the other hand, if it is judged that the value of the helical pitch
and/or the tube current is not changed in Step 26, it stands by
further, repeating the judgment for a certain period of time (Step
30). If the value of the helical pitch and/or the tube current is
not changed for the certain period of time, scanning prohibition
processing for forbidding the helical scan is performed (for
example, a prohibition flag is stood) and the prohibition
information is displayed on the imaging planning creation screen
(Step 31).
Since the operator is urged to change the helical pitch and/or the
tube current according to the changed number of slices in the
middle of making the imaging plan, the imaging conditions can be
set certainly and it is enabled to suppress the degradation of
quality-of-image or the increase of the X-ray doze.
Next, the third example of the second embodiment will be explained
with reference to FIGS. 20 and 21. FIG. 20 shows the alert
(warning) processing at the time of changing the reconstruction
thickness of the image in the middle of the imaging planning
creation processing mentioned above. Specifically, the host
controller 110 performs Steps 41 to 43 which are the same
processing as Steps 11 to 13 in FIG. 12 mentioned above. In Step
43, if it is judged that the reconstruction thickness is changed
into another value, the host controller 110 displays, on the
imaging planning creation screen, the alert (warning) information
which urges the operator to confirm the value of the image pitch
that is relevant to the reconstruction thickness (Step 44).
This warning is performed in various kinds of modes, such as
changing the background color of the window of the reconstruction
thickness, blinking the value of the reconstruction thickness,
generating a sound with it, and displaying a pop-up message, as
shown in FIG. 21. The example shown in this FIG. 21 shows that the
reconstruction thickness is set 1 mm and the image pitch is set 1
mm at the beginning for the helical scan, but the operator changes
the reconstruction thickness to 0.5 mm, then the background color
of the window of the image pitch. After the alert, the host
controller 110 judges whether the value of the image pitch is
changed by the operator or not (Step 45). Subsequently, in a
certain period of time, if such value is changed, the host
controller 110 judges the value is appropriate or not with
reference to a table, for example (Step 46).
If the value is appropriate, it stands by to next processing
timing, and processing is returned to Step 43 (Steps 47 and 48). On
the other hand, if it is judged that the value of the image pitch
is not changed in Step 45, it stands by further, repeating the
judgment for a certain period of time (Step 49). If the value of
the image pitch is not changed for the certain period of time,
scanning prohibition processing for forbidding the helical scan is
performed (for example, a prohibition flag is stood) and the
prohibition information is displayed on the imaging planning
creation screen.
Since the operator is urged to change the image pitch according to
the changed reconstruction thickness in the middle of making the
imaging plan, the imaging conditions can be set certainly and it is
enabled to suppress the degradation of quality-of-image or the
increase of the X-ray doze as same as the second example.
The present invention is not limited to the above embodiment, and
various modifications may be made without departing from the spirit
or scope of the general inventive concept. For example, in the
above-mentioned embodiment, although ROTATE/ROTATE type where an
X-ray tube and a detector rotate around the patient is explained,
(STATIONARY/ROTATE) type where the array of many detection elements
are arranged as the shape of a ring and the only an X-ray tube
rotates around the patient may be used. Moreover, although the case
where the about 360 degrees projection data around the patient is
used for the reconstruction is explained in the above embodiment,
any reconstruction algorithm like a half scan where 180 degree and
view angle projection data may be used. Furthermore, although the
above-mentioned embodiment explains the indirect conversion type
detector where the X-ray changes into the light with the
scintillator and the light is converted to into an electric charge
with light-electronic conversion elements, such as a photo-diode,
the direct type detector where the X-ray directly changes to an
electric charge with the semiconductor material where the electron
hole pair is generated and moves each side may be used. Moreover,
in the above-mentioned embodiment, although one X-ray tube type
X-ray CT apparatus is explained, two or more pairs of an X-ray tube
and an X-ray detector, so-called multi X-ray tube type X-ray CT
apparatus may be used.
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